The term “hearing aid”, “hearing instrument” or “hearing device”, as understood here, denotes on the one hand hearing aid devices that are therapeutic devices improving the hearing ability of individuals, primarily according to diagnostic results. Such hearing aid devices may be Outside-The-Ear hearing aid devices or In-The-Ear hearing aid devices. On the other hand, the term stands for devices which may improve the hearing of individuals with normal hearing e.g. in specific acoustical situations as in a very noisy environment or in concert halls, or which may even be used in context with remote communication or with audio listening, for instance as provided by headphones.
The hearing devices addressed by the present invention are so-called active hearing devices which comprise at the input side at least one acoustical to electrical converter, such as a microphone, at the output side at least one electrical to mechanical converter, such as a loudspeaker, and which further comprise a signal processing unit for processing signals according to the output signals of the acoustical to electrical converter and for generating output signals to the electrical input of the electrical to mechanical output converter. In general, the signal processing circuit may be an analog, digital or hybrid analog-digital circuit, and may be implemented with discrete electronic components, integrated circuits, or a combination of both.
Many hearing aids comprise more than one microphone in order to allow directional hearing. They may also have additional signal sources such as telecoils, audio input lines and wireless receivers for amplitude or frequency modulated (AM or FM) signals. In order to automatically select a signal source that is appropriate for the user's current hearing situation, various approaches exist: Telecoils and the processing of telecoil signals are e.g. activated by a reed relay that is operated by a small magnet attached to a telephone receiver as described in DE 31 09 049 C2. Audio input processing may be enabled by a contact which is mechanically activated when a corresponding input device such as an audio shoe is attached to the hearing aid.
In order to eliminate the need for dedicated electromechanical devices, DE 101 46 886 proposes to constantly digitise audio signals from two potential signal sources. The digitised signals are analysed by a classification algorithm running on a digital signal processor (DSP), resulting in an indication which signal may carry relevant acoustic information. The respective signal or a mixture of signals is then fed to the output speaker.
An important design criterion for components of hearing devices is the electric power consumption.